In a related-art radial line slot array antenna, a slot pattern is provided such that desired radio waves can be emitted. One of these types of antennas is described, for example, in Japanese Laid-Open Patent Publication No. H05-67918 (Patent Literature 1).
In another related-art radial line slot array antenna, a plurality of slots are arranged in concentric circles which are spaced apart in a radial direction by distances corresponding to a plurality of frequency bands, respectively. One of these types of antennas is described in Japanese Laid-Open Patent Publication No. H05-83029 (Patent Literature 2).
In another related-art radial line slot array antenna, a plurality of slots formed along circular or semi-circular arcs such that the distance between the slots becomes sequentially smaller along the circumferential direction in order to make the radiated power uniform. One of these types of antennas is described in Japanese Laid-Open Patent Publication No. H05-283931(Patent Literature 3).